1. Field of the Invention
The present invention relates to a liquid crystal display device which displays an image by allowing light from a backlight to pass through a substrate on which thin film transistors (TFTs) are formed.
2. Description of the Related Art
In a liquid crystal display device, there has been known an active-matrix-type liquid crystal display device which performs a display control of pixels using thin film transistors (TFTs). Such a liquid crystal display device is constituted of a liquid crystal panel including a TFT substrate on which thin film transistors are formed in a matrix array, and a backlight which supplies light to the liquid crystal panel.
As the device structure of the thin film transistor, there has been a bottom gate structure in which a gate electrode is arranged below a semiconductor film made of amorphous silicon (a-Si), polycrystalline silicon (poly-Si) or the like. FIG. 9A is a plan view showing one example of a thin film transistor having the conventional bottom-gate structure, and FIG. 9B is a cross-sectional view of the thin film transistor shown in FIG. 9A. As shown in FIG. 9B, a gate electrode GT is arranged on a transparent substrate GA and, further, a semiconductor film AS is formed over the gate electrode GT.
FIG. 10A is a plan view showing one example of a thin film transistor having the conventional bottom-gate structure, and FIG. 10B is a cross-sectional view of the thin film transistor shown in FIG. 10A. As shown in FIG. 10A, a semiconductor film AS is formed inside the gate electrode GT as viewed in a plan view, and the semiconductor film AS is shielded from light of a backlight radiated from a side below a transparent substrate GA. Accordingly, such a thin film transistor shown in FIG. 10A can suppress the occurrence of an optical leak current which deteriorates image quality of a liquid crystal display device.
JP-A-5-313192 discloses, as shown in FIG. 12 and the like in the same document, a thin film transistor where the whole semiconductor film is shielded from light of a backlight by a gate electrode.